1 Answer
1

Your Element.extend(element); works, although the most common way is to just pass it through $():

var extended = $(document.getElementById('billing:postcode'));

But note that single elements don't have the Prototype invoke method, which is the real problem you're running into. :-) invoke is part of Enumerable, which only applies to lists of elements, not individual ones — its purpose is to call a given function on each element in the list. Rather than calling invoke, just call the function you're trying to invoke directly.